Liquid crystal display devices are actively introduced in the field of such OA (office automation) instruments as personal -computers and word processors since the display devices can be driven at a low voltage, are light in weight, and provide a high image quality. As the liquid crystal display devices used in these applications, devices of twisted nematic mode in which the direction of alignment of nematic liquid crystal molecules is twisted by 90.degree. between the surface of a pair of upper and lower electrode substrates are generally employed. Liquid crystal display devices in which twist angle of liquid crystal molecules is increased to such a large angle as 180.degree. to 300.degree. are known as super twisted nematic mode. Besides, in order to perform matrix display or color display, development of liquid crystal display devices of active matrix type twisted nematic mode using a MIM (metal-insulating layer-metal) circuit element by which ON-OFF of a large number of pixel electrodes can be performed or using a TFT (field effect type thin film transistor) circuit element became active in recent years.
In Laid-open Japanese Patent Publication No. Hei 2-2525, a technology is disclosed in which parallel X-rays are irradiated to a substrate on the surface of which a X-ray resist layer is provided, and then the substrate is immersed in a developer and a rinse to increase the pretilt angle of liquid crystal molecules to be formed on the surface of the substrate. According to the technology disclosed in the publication, an X-ray resist layer is exposed to X-rays and immersed in a developer and a rinse to form microscopic projections and depressions on the surface of the X-ray resist layer thereby to align the liquid crystal molecules.
In Laid-open Japanese Patent Publication No. Hei 8-211622, an example of apparatuses for coating a thin film employing the effect of destaticizing with a soft X-ray is disclosed.
On the other hand, in Laid-open Japanese Patent Publication Nos. Hei 8-45695 and Hei 8-124695, static eliminating apparatuses using a soft X-ray are disclosed. Apparatuses disclosed in these publications are principally to blow the air which is ionized with a soft X-ray, to objects.
In Laid-open Japanese Patent Publication No. Hei 8-50293, which was published based on an application filed a few years ago by the present inventors, methods for producing liquid crystal display devices comprising irradiating a soft X-ray to an alignment film in a gas after a rubbing treatment are disclosed. More specifically speaking, in the publication, a technology is shown in which a soft X-ray is irradiated to an alignment film activated by a rubbing treatment, to reduce the surface energy of the alignment film thereby to prevent uneven displays from occurring in liquid crystal display devices.
Since it has entered upon a period of multi-media and many letter displays and diagrammatic displays have been sought, liquid crystal display devices are inevitably proceeding toward expanded screen size, large number of pixels, and fine displays. In keeping with such circumstances, production yield of liquid crystal display devices is on the trend of being lowered to some extent. As the factors which affect the lowering of production yield, occurrence of such uneven displays that regions having a different contrast or different chromaticity appear in a part of a screen, and happening of pixel defects such as a white defect in which the pixel becomes rid of light at the time of black display and a black defect in which the pixel does not transmit the light at the time of white display can be mentioned.
In the steps for producing liquid crystal display devices, many particles such as the so-called dusts, reaction products, and broken pieces of the substrates or surrounding materials are considered to occur. The particles slip into liquid crystal display devices and become a principal cause of the uneven displays and pixel defects described above. With the advance of cleaning technology, large particles have come to be seldom slipped into the devices. However, it is still difficult to completely remove extremely fine particles such as fatty acids generated from human bodies.
Recently, in order to remove the extremely fine particles, dry washing treatments using a nozzle capable of jetting air in such a way as performed with wipers, and wet washing treatments using pure water or an organic solvent are being used. However, it is difficult to completely remove the extremely fine particles by the dry washing treatments. With the wet washing treatments, it is pointed out that an extremely small amount of impurities are included even in washing liquids, and it is also difficult to completely remove the impurities.
On the other hand, it is known that such an extremely high static electricity as 6 to 10 keV is generated in the steps for producing liquid crystal panels, particularly at the time of conveying glass substrates, or in a thin film coating step or the like. As the result, the particles come to readily adhere on the substrates by the generated static electricity, and this fact has become a leading cause of lowering the production yield of liquid crystal display devices. In connection with the static electricity, whereas a method wherein a humidifier is used to increase humidity up to 60 to 70%, or a method wherein an ion generating apparatus is installed is being used to cope with the adhering of particles described above, such methods are still insufficient. As detrimental effects by the static electricity, disconnection or short-circuit of electrodes due to electrostatic breakdown, malfunctioning of active devices, and the like can be mentioned.
As described above, in order to increase the yield in the production of liquid crystal display devices, it is important to reduce the number of particles in production facilities, to repress the adhering of particles to substrates caused by static electricity, and to remove the adhered particles by washing. However, according to conventional methods, it was difficult to fundamentally solve the problems.
In the steps for coating or forming such a thin film as a photoresist, insulating film, and alignment film, it is difficult to remove, even by washing treatments, the particles which were adhered on the surface of a substrate in the steps of coating, evaporating, and drying, since the solvent is evaporated and the film thus formed is dried in the steps after a liquid having a flowability was applied on the surface of the substrate; and the difficulty has become a particularly serious problem.